Friday, May 28, 2010

The Threat of Sperm

I recently listened to an episode of Radio Lab, an NPR radio program, about reproductive physiology and how it's evolved in various animal species. It's a fascinating one-hour episode that you can listen to here: http://www.wnyc.org/shows/radiolab/episodes/2008/11/21. If you need convincing, here are some highlights/spoilers:

Performing DNA tests on bird eggs from the same nest revealed multiple paternity. As a result, further research into the monogamy of female species was done, and it was found that, in fact, the majority of animals are promiscuous.

Not only do male animals have to compete with each other in order to copulate with females, but their sperm within the females also needs to compete with other males' sperm within the females. Thus, many species have evolved in ways to better the chances that their sperm will be the winning sperm in inseminating the females.

The penis of a dragonfly is covered in backwards-pointing spires. It brushes and collects remnant sperm within the female during mating. Before ejaculating, the male will pull out, shake off all the other male sperm, then reinsert and ejaculate himself within the female.

Mating among ducks occurs as rape. So female ducks have evolved to have very complex vaginas. The longer the male penis in a species of duck, the more complex the female vagina. Their vaginas have off-ramps that lead to dead-ends meant to deflect the males from inseminating them. The main path that leads to the uterine tubes ends in a long, corkscrew-like spiral. Should the male make it through to this main path, the female can contract the spiral to keep the sperm out.

Human female bodies store sperm for up to a week until the woman ovulates and can make use of the sperm.

There are species in which the males have died out, and the women live on. This episode discusses what it would take for human females to dispense with human males.